THE BRITTLE DEFORMATION SEQUENCE AT DEAD INDIAN HILL AND THE HEART MOUNTAIN DETACHMENT

G. Graham Ellsworth, Mervin J. Bartholomew
2017 unpublished
The Heart Mountain Detachment in northwestern Wyoming is one of the largest terrestrial mega-scale gravity-slides. Its emplacement followed the Laramide Orogeny and was contemporaneous with the Eocene magmatic activity in the Absaroka Volcanic Province. Analysis of fracturesets (joints and faults) from Cambrian to Eocene strata provide the framework for deciphering the regional brittle fracture sequence. Measurements are from "pinned to basement" strata below the detachment and a small klippe
more » ... nd a small klippe above the detachment horizon at Dead Indian Hill, the Eocene Willwood Formation in the Bighorn Basin, and the classic White Mountain location. Laramide fracture-sets at Dead Indian Hill progressively rotate clockwise from north to northeast. The angular and abutting relationships of Laramide joint-sets also occur in the klippe and indicate passive transport of hanging-wall Laramide fracture-sets during the detachment in the Eocene, only after corrections for bedding dip, slope and a clockwise rotation of ~30 o around a vertical axis. Laramide fracture-sets were not found in any Eocene age strata. Eocene fracture-sets progressively rotate counterclockwise from the northwest to the west. The Heart Mountain Detachment fractures are defined by joint-reactivations as strike-slip faults which rotate 28 o counterclockwise from the oldest Eocene fracture-set. Abstract Dead Indian Hill: Eocene Fracture-Sets: Pre-Heart Mountain Detachment Fracture Sets within the Allochthon: a small klippe on the western hill slope
doi:10.1130/abs/2017rm-293140 fatcat:2hejzdswyvbgfajfqy2k3j7lnm